Abstract: Although much progress has been made in detecting and treating cancer, disseminated metastatic cancer remains the leading cause of death in patients with advanced stage carcinoma. Ovarian cancer is such a disease, with 90% of all fatalities arising from microscopic, difficult-to-visualize lesions that often grow to resist treatment. Ovarian cancer is particularly deadly due to a lack of early symptoms and its propensity to extensively coat the tissues and organs throughout the abdomen with occult metastatic disease. Frustratingly little is known regarding how these microscopic lesions resist treatment in vivo due to their widespread nature and sub-clinical size. A lack of oxygen, known as hypoxia, is a major cause of treatment resistance in cancer, and is likely responsible for resistant ovarian disease. The goal of this New Innovator proposal to is overcome hypoxia-induced resistance by developing a new microscopic and translational imaging approach for battling metastatic disease. This imaging-based platform will use three independent and highly complementary methods to understand treatment response and overcome hypoxic treatment resistance. A new multimodal hyperspectral microendoscope will be developed to address the challenge of visualizing micrometastatic lesions in vivo and wil be specificaly tailored to image both ovarian micrometastatic hypoxic state and response to treatment. To map the exact relationship between hypoxia and therapeutic response, we will use a 3D in vitro model of micrometastatic ovarian cancer to carry out high-throughput, microscopic, multiparametric visualization experiments. Furthermore, to overcome hypoxia-induced treatment resistance, we will develop an oxygen-independent and tumor-localizing photodynamic therapy regimen, first to be tested in vitro, and then translated and visualized in vivo using the microendoscopy platform. By building our knowledge of treatment response and resistance from the bottom up, these combined methods form the foundation of a fresh, innovative approach towards understanding and ultimately defeating treatment-resistant micrometastatic disease. Public Health Relevance: Cancer that becomes metastatic is too often fatal due to the spread of numerous microscopic lesions that can grow to become treatment resistant. The goal of this proposal is to address a major contributor to treatment resistance in ovarian cancer through an innovative microscale visualization approach that not only detects and visualizes micrometastatic treatment response, but also overcomes treatment resistance with new therapeutic regimens. By building an understanding of these small and evasive lesions, and using this knowledge to defeat treatment-resistance disease, this proposal aims to significantly improve the lives of patients suffering from advanced metastatic cancer.